This invention relates to methods and devices for sharpening woodworking tools, including chisels, plane blades, carving tools, and knives. It relates, in particular, to rotating grinding, buffing, lapping, and polishing wheels and belts and other powered tool sharpening apparatus.
Most woodworking hand tools require sharpening, especially new tools. Chisels, plane blades, carving tools, axes, drawknives, and other tools all need to be prepared for use by grinding and polishing two intersecting surfaces to create a keen cutting edge or arris. Tool use dulls and sometimes damages this arris, making periodic re-sharpening necessary. Many tool sharpening devices and techniques have been developed, but tool sharpening and re-sharpening remains difficult for many tool users because of the substantial practice, skill and time needed to utilize many sharpening devices and techniques successfully. Additionally, widespread unfamiliarity with well-sharpened tools makes it difficult for many tool users to accurately judge the quality of sharpening results.
All relevant sharpening techniques involve abrading tool surfaces with abrasive materials, such as natural or man-made stones, or with abrasive particles deposited on another substrate. Among existing products intended for sharpening woodworking hand-tools are high-speed, xe2x80x9cdryxe2x80x9d grinding wheels that do not use lubrication and low-speed xe2x80x9cwetxe2x80x9d wheels that use lubrication on the wheel surface, typically water. Some of these products utilize relatively large diameter vertical wet or dry grinding or honing wheels, where the wheel edge is the principal working surface. Others utilize horizontal wheels where one face of the wheel is the principal working surface. A variety of abrasive xe2x80x9cstonesxe2x80x9d usually having flat surfaces are available for manual sharpening.
One of the challenges associated with use of all abrasive wheels and manual stones is wheel or stone surface shape. Wear during use invariably causes stone or wheel surfaces to become uneven, requiring dressing of those surfaces to restore the desired shape and often resulting in changes in the distances between such surfaces and associated tool guides and rests. These changes in system geometry as a result of stone wear, and shortcomings of existing tool guides and rests make it extremely difficult or impossible with most existing devices to achieve reproducible sharpening geometries that produce reproducible sharpening angles on the tools being sharpened. Depending on the type of tool, the way it was manufactured, the materials from which it was manufacture and its intended use, certain specific bevel angles are required for the cutting edge. Once a specific, successful bevel angle is achieved, the user will want to reproduce that same angle as closely as possible when the tool requires resharpening.
Additionally, existing sharpening products have no provision for grinding and polishing both surfaces of many cutting tools such as plane blades and chisels, because they have no provision or only inadequate provisions for grinding and polishing or xe2x80x9clappingxe2x80x9d the back of such tools, which is required successfully to sharpen such tools.
To be practical and effective, any abrasive operation like tool sharpening must use several grades of abrasives to progress from shaping and forming of the tool""s surface to the desired level of surface finish. The more highly polished the surface finish needs to be, the more abrasive steps are required. Typical tool sharpening requires a broad range of abrasive grades because sharpening starts with formation of the principal bevel or back surface by grinding and ends with polishing to a mirror finish.
Among other desiderata that result from the considerations mentioned above, a sharpening system desirably should provide:
a wide range of abrasive grades
a highly functional tool holding and guiding system
controllable, reproducible system geometry, particularly relative to the relationship between the tool holder and guide (and therefore the tool being sharpened) and the abrasive surface;
an absolutely flat abrasive surface
easily renewable abrasive surfaces
flexibility in accommodating a wide range of tool sizes and shapes
modest generation of heat in the tool to avoid metallurgical damage
safe operation
speed.
These and other desirable objectives associated with tool sharpening are achieved by this invention.
This sharpening system combines a relatively slowly rotating horizontal turntable and, alternatively, either a rotating vertical grinding wheel or belt. The belt and/or wheel may be used for grinding, shaping, and in some cases, sharpening, a wide variety of woodworking tools in a relatively conventional manner. The rotating turntable is topped, during use, by a platter to which abrasive has been attached by bonding a plastic or fabric sheet coated with abrasive or a disk of cloth charged with abrasive. Abrasive may be positioned on both sides of the platter, making the platter reversible, and multiple platters may be used. Relatively slow turntable rotation limits heat buildup during use.
A tool such as a plane blade or chisel to be sharpened (and already having a properly lapped back) is secured in a tool holder that rests and travels against a repositionable tool rest or tool guide fixed in position relative to the turntable in order to form a main bevel on the tool at a desired angle. That bevel is formed utilizing a first grade of abrasive affixed to a platter having a particular thickness and that is mounted on the turntable. A second, thinner platter having a finer grade abrasive is then mounted on the turntable. Contact between the tool and the abrasive on the second platter (without changing any other aspect of the system or tool holder geometry) then automatically produces a micro-bevel to complete tool sharpening because the tool contacts the abrasive on the thinner platter at a slightly greater angle. Thus, abrasion occurs only at the very front of the bevel adjacent to the arris where it is needed to hone the cutting edge or arris. This minimizes the amount of abrasion required, and consequently lengthens the working life of the abrasive and reduces the time needed for sharpening.
The back of a tool such as a plane blade or chisel may be lapped flat against an appropriate grade of abrasive mounted on a platter positioned atop the rotating turntable.